1. Field of the Invention
This invention relates to improvements in an intake system for a V-type internal combustion engine, employing inertia supercharging and resonance supercharging.
2. Background of the Invention
It is well known in the art to employ an intake air supply method in which intake air charging efficiency is improved under the effect of inertia supercharging and resonance supercharging. The inertia supercharging is caused by intake air pressure vibration which is generated such that negative pressure generated near intake ports at an air intake initial time propagates at sonic velocity toward the end of intake pipes and returns toward intake ports upon being converted to positive pressure wave. In other words, by matching the cycle of intake air pressure vibration and the cycle of intake valve opening and closing so that the positive pressure wave is transmitted to the intake valve immediately before closing of the intake valve, air generating the positive pressure wave is thrusted into the cylinder under its inertia.
The resonance supercharging is made by a pressure rise upon resonance which is caused when engine speed harmonizes with the resonance frequency of the whole intake system upon generating intake air vibration through a resonance pipe between two groups of cylinders which do not generate intake air interference with each other.
Such an intake system of the V-type engine, employing inertia supercharging and resonance supercharging is disclosed, for example, in Japanese Patent Provisional Publication No. 62-101820. This will be roughly discussed with reference to FIGS. 7A and 7B. In FIGS. 7A and 7B, two groups X, Y of cylinders are fluidly connected with two independent distribution chambers 31, 32 through long main air intake pipes 33 and short by-pass air intake pipes 34. Additionally, the respective two distribution chambers are fluidly connected with each other through a communication passage 35. Each by-pass air intake pipe 34 and the communication passage 35 are suitably opened and closed. The distribution chambers 31, 32 are fluidly connected with a gathering chamber 37 through air intake passages 36 which are independent to each other and extend from one end to the other end of each of the distribution chambers 31, 32. The gathering chamber 37 is provided with a throttle body having a throttle valve 39, in which intake air inducted through an air filter (not shown) is controlled in amount by the throttle valve 39 and thereafter introduced into the cylinders.
However, in the above conventional intake system of the V-type engine, the distribution chambers 31, 32 are disposed between the banks, and the communication passage 35 between the distribution chambers 31, 32 is disposed horizontally between the banks in such a manner as connect the distribution chambers 31, 32 at the longitudinal intermediate portions. Additionally, the main intake pipe 33 is also disposed horizontal between the banks. The thus arranged intake system has the following disadvantages: The main air intake pipes 33 are relatively short and difficult to be further prolonged, and therefore a sufficient inertia supercharging cannot be obtained. Additionally, since the communication passage 35 is disposed horizontal between the banks, the intake passages 36 disposed above the communication passage 35 is unavoidably raised thereby raising the overall height of the engine and deteriorating a vehicle design. Furthermore, the gathering chamber 37 cannot be expanded upwardly under the restriction of the overall height of the engine, and cannot be expanded downwardly because the communication passage 35 and the main air intake pipe 33 are disposed horizontally between the banks. Consequently, it is difficult to form the gathering chamber large in volume. As a result, a sufficient inertia charging cannot be obtained in low and medium engine speed operating ranges similarly to in the above case of difficulty of prolonging the main air intake pipe 33.